A view of the geology of the Northern Rivers of New England, New South Wales. Includes thoughts on the formation of the regions volcanoes (Mount Warning, Ebor and others), groundwater, the Clarence Moreton Basin, recent sedimentation, gas (including coal seam gas), mineralization in the eastern part of the southern New England Orogen and more.
What is the geological influence in the Northern Rivers and New England areas of Australia that provide us with the beauty and diversity we see today?

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Monday, 17 February 2014

What is CSG?

What is CSG? Very simply Coal Seam Gas (CSG) is natural gas obtained
directly from coal seams. Another common name for CSG is Coal Bed Methane (CBM). Like most natural gases, the chemical components of
CSG are dominated by methane. Though some higher end hydrocarbons such as ethane
or propane may also be present. Carbon dioxide and nitrogen are usually significant components of CSG too and the
higher the proportion of these non-hydrocarbon gases the lower the quality of
the gas. This simple summary does not tell us very much, so more detail is
required.CSG is an interesting gas when compared to ‘conventional’
gases. ‘Conventional’ gas has migrated away from coal and organic rich
sedimentary rocks into other porous rocks. The gas is then held in place by impermeable
layers. What makes CSG different is that the gas has only migrated very small
distances (if at all) to natural pore spaces such as fractures (cleats) in the
coal layers. These pore spaces usually contain natural water that was left in
the coal when it was laid down or water that subsequently migrated into the
coal seam. The water associated with the coal seam is very important because it
is actually the pressure of the water in the coal seam that keeps the gas in
place. It is the hydrostatic pressure that keeps the gas in place.In open cut or underground coal mining, CSG is a curse. It
is considered a waste product and an explosion hazard. It is therefore vented
as much as possible to make the coal mines safe to work in. The recent Pike
River Mine explosion in New Zealand is an example where the failure to vent
enough CSG caused a tragedy. As water is removed from coal mines the chances
for gas mobilisation increases due to the above mentioned effect of hydrostatic
pressure. This further increases the risk of explosion in coal mines.

Idealised relationship between CSG and water production

Natural gas became more popular for domestic and industrial
use over the last few decades and the means to transport it economically became
available (e.g. LNG). This meant gas that was often a by-product of the
oil and coal industries became important in its own right. This led to people searching
for gas sources in their own right, CSG included. Petroleum engineers realised if you reduce the pressure of water in a coal seam and collected the gas you could actually use the gas as a resource leaving the
coal in place. This means that drill holes can be placed into coal seams
and the water drawn out. The water drawn out (called formation water) is
actually a ‘by-product’ of the gas extraction process. The formation water is
the nuisance that needs to be removed to allow the gas to escape. This means
that a new gas well will produce very little gas at first and lots of ‘waste’ water.
As the water is drawn down the gas production increases and the water
production decreases. Interestingly this is the opposite of that which occurs
for ‘conventional’ gas, where waste water is a problem in the later stages of
production but not early on.Many people are concerned about CSG in Australia, particularly
in our northern rivers region. This concern is driven by the possible effect of CSG
extraction on beneficial groundwater. The use of techniques such as
hydraulic fracturing that may be used to increase or prolong gas production is also raised as a concern. To
keep this post short I will cover both of these issues in future. However, I
will suffice to say that there is evidence that groundwater can be
affected during CSG extraction despite producers trying not to have any impact. These are particularly noted in certain geological formations. There
are also situations where there is no impact on important aquifers too. This matter is clearly quite complex and a one size fits all understanding does
not apply very well. Hopefully, my future posts will tease the details out a
little bit more.

8 comments:

As both you and I know there is a lot of resistance to CSG mining and maybe it is a good thing too. What I really like about your CSG posts is that you give a non-polarised view of the subject and simply state the process warts and all. I have directed quite a few people to your site so they can understand that some of what is going on for themselves. Good on you and always looking forward to your next post.Dylan

Let me second that endorsement. It's fundamental to get some basics on the scene underground so we can judge the quality of claims made by opponents and proponents of CSG.

Sadly, the gas rush is getting a long way ahead of knowledge and monitoring capability in Queensland. I hear from insiders that it's basically open slather in the Great Artesian Basin, and groundwater monitoring is many years behind: there are relatively speaking just a handful of monitored sites compared with the many thousands of wells sunk, and reporting quality is also inconsistent.

Hi Nick, thank you for a second endorsement! I'm glad that I seem to be able to help.

Though I share much of your sentiment about the Great Artesian Basin, I did say in the last part of the post that the degree of risk is different from place to place. For example one of the big risks of CSG production in the GAB is the reduction in pressure head of aquifers. This reduction in pressure head can affect the discharge areas such as the ecologically sensitive spring mounds in desert Queensland and South Australia. That situation does not apply in the Northern Rivers. However, I'm sure there are things that are risks in our region that don't apply in the GAB too!

Every place is different and therefore the issues are almost always different too. That can be a good thing... and it can be a bad thing too.

Fantastic insight to the CSG issue and extraction, Rod. I hadn't known much about this, and I really appreciate your objective outline of the process. As with those above, I like to share your posts, as what you write as it is easy to understand by non-geologists.

Thank you for writing about this. I had begun to despair over whether it was possible to find science based information, that is comprehensible to the layman as regards CSG in New South Wales. I appreciate the balanced viewpoint you've provided (and understand your circumspection in regards to the politically incendiary nature of CSG). It's a pleasure to read your blog, thank you for writing!

A pleasure to have you visit and comment. I have only done a few other blog posts on CSG due to me being too timid to delve into the details much but feel free to look at my other posts this topic and on natural gas in general. A summary of posts can be found here:

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About Me

I have tertiary qualifications in earth science and I have worked in areas of exploration geology, water quality management, environmental engineering, bushland management, groundwater resource studies, contaminated land and mapping programs. This has been done in private industry, local government and state government.

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